For the purpose of colored relief image formation, it has been proposed to use colored materials (especially carbon) dispersed in the non-sensitive layer of a two layer tannable construction such as that shown in U.S. Pat. No. 3,364,024. Of the various tanning developers, comprising pyrogallol, catechol, hydroquinone and its derivatives and gallic acid, as described, for example, by R. B. Pontius in PSA Journal, Section B, September 1951, pages 76-79 and by A. G. tull in The Journal of Photographic Science, Vol. 11, 1963, pages 1-26, the hydroquinone and some of its derivatives have been described as the most useful or even the only useful substances for satisfying the material and method requirements as heretofore stated.
In spite of this, and as already stated, tanning development methods have not found significant practical application. As these methods have always been regarded as a means for reducing silver consumption in the photographic industry, and considering the considerable cost increase undergone by silver in the course of time, it can be deduced that such methods do not give satisfactory results.
The conclusion of certain experiments and technical considerations made by the applicants was that constructions with the emulsion layer below the pigmented layer did not seem promising because of the fact that the pigmented, non-sensitive layer (NSL) would absorb part of the exposure light and thus present a low efficiency system which would be remedied only by higher silver contents. Likewise, although using a top coat of emulsion over the pigmented layer allows for smaller silver quantities, the reliefs obtained were not as sharp as required. The use of separate elements with an emulsion on one and a pigmented layer on the other is too complicated to be of commercial interest.